Friday, January 31, 2014

A Look Back at the #WinterMess

The snow that everyone graved finally came to the Midlands.  The same storm system that affected Birmingham and Atlanta also affected Columbia, SC.  Rain and sleet began to fall before noon on Tuesday, but it wasn’t enough to measure and didn’t cause any problems.  The lower atmosphere was quite dry so that it would take hours of light precipitation to moisten the atmosphere enough to allow for any significant precipitation.

Finally a band of rain/freezing rain moved across the southern half of the Midlands just before dark.  This was followed by snow in the northern part of the Midlands.  It eventually reached Columbia in the form of freezing rain.  At WLTX we pick up an ice accumulation of 1/10 of an inch before the precipitation changed over to snow.  The southern third of the Midlands saw ice accumulations of a ¼ to ½ inch.

The air was chilled by the rain/sleet/snow mix and temperatures fell below freezing over all of the Midlands shortly after sunset.  The precipitation changed to snow which fell mainly from 7:30 p.m. to about 2 a.m. across the Midlands.  Snow ended from west to east and the amounts didn’t vary a great deal across the Midlands.

A map of the midlands of South Carolina showing total snow depth as of Wednesday morning January 29, 2014.  This is from preliminary data.  Click on the image for a larger view.  Image Credit: NOAA/NWS/CAE.

Amounts were generally 2 to 3 inches across much of the area.  It was a wet snow which made for great snowmen and snowball fights.  Here is a view of the region from the satellite the next day:

A visible satellite view from Wednesday January 29, 2014.  The solid white area at the bottom of the picture are clouds for the most part.  Elsewhere skies are clear and the white areas are snow on the ground.  Click on the image for a larger view.  Image Credit: NASA.

Skies cleared late Wednesday and calm conditions developed overnight.  In addition, the snow cover allowed for good radiational cooling to occur.  This allowed temperatures to drop to very cold readings by Thursday morning.  The temperature at the National Weather Service Forecast Office in Columbia was 13° F for the low.  The lowest temperature occurred at Cedar Creek (northern Richland County) with 6° F.

We are fortunate to have a mesoscale network of sensors around Richland County.  This network showed how temperatures can vary on just a county scale.  Below are the low temperatures for Thursday morning:

Low temperatures around Richland County, SC, for Thursday morning on January 30, 2014.  Click on the image for a larger view.  Image Credit: Ken Aucoin/ RC Winds.

How well was this forecast?

Daniel Bonds and I spent a couple of hours Sunday afternoon evaluating the many different models.  The GFS (American) model did the best in capturing the ice accumulation and snow accumulation.  It wasn’t perfect, but it did the best job.

Our own in-house model (RPM) did the worst, but it was greatly influenced by the American WRF model.  Also, the European model was too cold which led to high snowfall totals and no ice.  The European model was forecasting snowfall of about 7 inches while the WRF was forecasting about 15 inches for Columbia.  These were unrealistic in my view given the dynamics of the atmosphere.

I suspect that this tainted some of the local forecasts of snow.  I frequently saw forecasts of 3 to 5 and 5 to 7 inches of snow.  Our forecast for 2 to 4 inches of snow hit the mark for the central Midlands.  However, our view of closer to 4 inches for the northern Midlands was too high.  The forecast of 1 to 2 inches of snow for the southern Midlands worked, but was a little low in places.  Our forecast for ice accumulation for the southern Midlands was spot on, but a little high for the central Midlands.

You can see the forecasts from the GFS model in the previous two posts.  I did not make a map of forecast snow, but talked in general terms.  When you have a storm producing a mix like this one, timing is everything.  Freezing rain and sleet tend to compact the snow leading to smaller snow depths.  An all snow event would likely have produced amounts in the 3 to 4 inch range.

We weathered the storm much better than cities to our west.  The situation in Atlanta has received the most media attention. I would direct you to two posts which cover it quite well.  The first post is from the president of the American Meteorological Society (soon to be past-president) and teaches at the University of Georgia.  The second post is from Bryan Norcross at the Weather Channel.

It will be warming into February and January will be a fading memory.  However, looking at the overall pattern for North America, the weather pattern is changing to something we have not seen since November.  Fasten your seatbelt, because it looks like it is going to be a wild ride.  Stay tuned!